Why stop at the penthouse when you can put something on the penthouse? Something like a traditional Chinese pagoda, an American style suburb, or even a mountain? Time to scale China's unusual—and often illegal—high rise structures.

Building on buildings is not a new thing in China—or in many cities with tall buildings. For years now, people have put pigeon coops on apartment and office buildings without permission. There have been shanty structures erected on apartment buildings—sometimes without permits. Below you can see illegally built pigeon coops in Fuzhou from 2010:

In the last few years, there have been an increasing number of "rooftop structures" (楼顶搭 or "lou ding da"). Or rather, there have been an increasing number of people noticing them. Some of the structures are built by the building owners and are apparently overlooked or ignored by the local governments.

The problem with these buildings are the obvious structural concerns. They were built without permits, so they might be hazardous, which worries residents. Sometimes people who build these structure even lock the rooftop fire escapes, blocking access to them. Then, there's a feeling that these structures are ignoring things like, well, rules. They are public displays of people doing whatever the hell they want.

Let's have a look at some of these rooftop structures from over the years. Note that not all of them are still standing.

Originally, this rooftop villa in Shanghai was supposed to be a pigeon coop, but other residents complained. So, the resulting structure ended up like this and is connected to the top floor apartment. The above photo is from 2010.

Spotted in Zhangzhou last year. A resident complained that someone was building an illegal rooftop home sans permit. The fire escape door to the roof was locked, too, blocking outside access.

Sometimes the rooftop structures are simple and relatively hard to spot, such as this 2011 rooftop metal housing, located in Fuzhou.

In Suzhou, there's a Jiangsu style complex on top of an apartment building. It's rumored to belong to a government employee and went up in 2007. On People's Daily, one of China's largest news sources, there's speculation that the structure went up illegally. That is, however, unconfirmed.

There's a shopping mall in Henyang with a rooftop apparently as big as several football fields. Twenty-five dwellings were built on top, but since they were built without a permit, the owner was repeatedly told to tear them down. According to BackChina.com, an agreement seems to have been reached: the houses cannot be sold, and thus, they won't be torn down. Demolishing the houses could possibly cause the building's roof to leak.

And here are four rooftop houses on a shopping center in Zhuzhou.

This is perhaps the most infamous rooftop structure in China. First erected in 2007, the opulent add-on mountain looks like something the last boss of a video game would inhabit. The building's owner, Zhang Biqing, has been building this rooftop lair for the past six years. However, the Beijing government ordered its demolition. Work began on that last Thursday, reports China Daily.